1. Field of the Invention
The present invention is related to artificial heart valves. More specifically, the present invention is directed to artificial mitral valve prostheses and method of implanting the prostheses leading to reduction of myocardial wall tension and the repair of mitral valve insufficiency.
2. Background
The mitral valve is a functional organ composed of multiple dynamically interrelated units. During cardiac cycle, the fibrous skeleton, the anterior and posterior leaflets, the papillary muscles, the chordae tendinea, and the ventricular and atrial walls all interplay to render a competent valve. The complex interaction between the mitral valve and the ventricle by the subvalvular apparatus (the papillary muscles and the chordae tendinea) is essential in maintaining the continuity between the atrio-ventricular ring (which is part of the fibrous skeleton of the heart) and the ventricular muscle mass, which provides for the normal functioning of the mitral valve.
Like all heart valves, the mitral valve exhibits two types of pathologies: regurgitation (i.e., abnormal leaking of blood from the left ventricle, through the mitral valve, and into the left atrium, when the left ventricle contracts) and stenosis (i.e., narrowing of the orifice of the mitral valve of the heart). Regurgitation is the more common of the two defects. Typically, either defect can be treated by surgical repair. However, surgical repair is not always feasible since many patients requiring mitral valve replacement are inoperable or deemed to pose too high a surgical risk because of extensive fibrosis, leaflets calcification, or massive chordae rupture. Further, such surgical procedures are traumatic. Additionally, surgical procedures can lead to an interruption of the mitral annulus-papillary muscle continuity, which accounts for changes in geometry mechanics and performance of the left ventricle. These problems are lessened by the emerging techniques for minimally invasive mitral valve repair, but still many of those techniques require arresting the heart and funneling the blood through a heart-lung machine, which can also be traumatic for patients.
In certain cases, the mitral valve cannot be repaired and must be replaced. Valve replacement can create additional problems including limitation of the mitral flow during exercise due to a small effective orifice area and high cardiac output imposed by a smaller size artificial valve as compared with the natural valve orifice area. Further, the rigid structure of an artificial valve prevents the physiologic contraction of the posterior wall of the left ventricle surrounding the mitral annulus during systole. Also, myocardial rupture can result from excision or stretching of the papillary muscle in a thin and fragile left ventricle. Additionally, chordae rupture can also occur due to the chordae rubbing against the artificial valve over time, leading to increased heart wall stress. It has been shown that severing the chordae can lead to a 30% reduction in chamber function. Thus, mitral valve replacement has a high mortality rate in very sick, chronic heart failure patients.
The chordae tendinea, which connect the valve leaflets to the papillary muscles (PM) act like “tie rods” in an engineering sense. Not only do the chordae tendinea prevent prolapse of the mitral valve leaflets during systole, but they also support the left ventricular muscle mass throughout the cardiac cycle. To function adequately, the mitral valve opens to a large orifice area and, for closure, the mitral leaflets have an excess surface area (i.e. more than needed to effectively close the mitral orifice). On the other hand, systolic contraction of the posterior ventricular wall around the mitral annulus (MA) creates a mobile D-shaped structure with sphincter-like function which reduces its area by approximately 25% during systole, thus exposing less of the mitral leaflets to the stress of the left ventricular pressure and flow.
It has been long postulated that the structural integrity of the MA-PM continuity is essential for normal left ventricular function. Recent evidence supports the concept that preservation of the subvalvular apparatus with the MA-PM continuity in any procedure on the mitral valve is important for the improved long-term quality and quantity of life following valve replacement. Maintaining the MA-PM continuity, thus, appears to provide a substantial degree of protection from the complications associated with valve replacement.
Therefore, what is needed is a mitral valve prosthesis and method of implantation that minimizes the traumatic impact on the heart while effectively replacing native leaflet function. A consistent, reproducible, and safe method to introduce a prosthesis into the mitral position in a minimally invasive fashion could be attractive for numerous reasons: a) it can treat both functional and degenerative mitral regurgitation (MR); b) it can treat mitral stenosis; c) it can offer a remedy to inoperable patients, high risk surgical patients, and those that cannot tolerate bypass; d) it can allow a broad range of practitioners to perform mitral valve procedures; and/or e) it can enable more consistency in measuring outcome.